The DC Metro area is full of great people! 
The Washington DCJCC works with several networks for adults over 35.

From 5 to 5
From 5 to 5—Socialize with 35-45 year olds!

From 5 to 5 is a volunteer-run group geared towards DC-area young Jewish adults who are 35-45 years old. This is a group for singles, couples, marrieds, parents--anyone who wants to meet new people and make new friends! You can find them on Facebook.
Feel free to create an event for the group and/or let the group coordinator Lauren Cranman know if you have any ideas.

3649 Singles Dinner in DC

Washington DC is a city of amazing restaurants and this network provides connections for single adults between the ages of 36 and 49 to get together and enjoy a different restaurant each month. If you are interested in joining a group for dinner at a restaurant or suggesting a new culinary diversion, please contact David Rose, Coordinator for 3649 Singles Dinner in DC with the subject “Add me to 3649 Dinner in DC for Singles!”  Include your full name, email address, phone number, age, and three restaurants in the DC Metro area you would like to recommend for future events (optional). 

Of a Certain Age

Of A Certain Age is an opportunity to meet other individuals who are 50 + for events that you will hear about through email announcements. If you would like to be on the email list for events contact Tybe Diamond at ibtybe@aol.com. Many individuals have reported making new friendships as a result of their attendance at various activities.